Intermetallic diffusion block device and method of manufacture

ABSTRACT

One embodiment of the present invention is directed to an under bump metallurgy material. The under bump metallurgy material of this embodiment includes an adhesion layer and a conduction layer formed on top of the adhesion layer. The under bump metallurgy material of this embodiment also includes a barrier layer plated on top of the conduction layer and a sacrificial layer plated on top of the barrier layer. The conduction layer of this embodiment includes a trench formed therein, the trench contacting a portion of the barrier layer and blocking a path of intermetallic formation between the conduction layer and the sacrificial layer.

BACKGROUND OF THE INVENTION

1. Field of the Invention

This invention relates generally to semiconductors, and moreparticularly to under bump structures having reduced inter-metallicformation.

2. Description of Background

A Controlled Collapse Chip Connection, or C4, is one type of mountingthat may be used for mounting semiconductor devices, such as integratedcircuits (IC's), Microelectromechanical Systems (MEMS) or othercomponents, to a wafer. C4 utilizes solder bumps instead of wire bondsfor the connection. The solder bumps are deposited on chip pads whichare located on a top side of a wafer during a final wafer processingstep. These solder bumps may be used to connect any type of circuit ordevice to the wafer.

Environmental legislation in Europe has specifically targeted the wideuse of lead in the electronics industry. The directives in Europerequire many new electronic circuit boards to be lead free by 1 Jul.2006, mostly in the consumer goods industry, but in some others as well.With lead-free proliferation driving development activities to focus onlead-free solders, other types of solder are now being utilized.

Many new technical challenges have arisen due to utilizing lead-freesolder such as tin. For instance, traditional leaded solders have asignificantly higher melting point than lead-free solders, which rendersthem unsuitable for use with heat-sensitive electronic components andtheir plastic packaging. To overcome this problem, solder alloys with ahigh silver content and no lead have been developed with a melting pointslightly lower than traditional solders.

Lead-free construction has also extended to components, pins, andconnectors. Most of these pins used copper frames, and either lead, tin,gold or other finishes. Tin finishes are the most popular of lead-freefinishes.

Having to use lead-free solders has given rise to a problem related tothe formation of intermetallics. The formation of intermetallics leadsto reliability concerns. The amount of intermetallic increase with timeand temperature can result in the degradation of the under bumpmetallurgy (UBM) interface. Many UBM structures now incorporate nickel(Ni) layers to prevent or reduce intermetallic formation by decreasingthe diffusion of copper into the solder bumps. For plated UBMstructures, the common practice is to sputter a copper (Cu) seed layerprior to plating. During reflow, solder ball wets expose the edge of thesputtered Cu layer. The intermetallic formation is then dictated by thediffusion path and can result in an effective decrease in UBM padadhesion. That is, if the sputtered copper layer is not effectivelyseparated from an upper sacrificial layer of the pad (typically formedof Cu), intermetallics may be formed and reduce the strength of the bondto the solder ball placed thereon.

SUMMARY OF THE INVENTION

One embodiment of the present invention is directed to an under bumpmetallurgy material. The under bump metallurgy material of thisembodiment includes an adhesion layer and a conduction layer formed ontop of the adhesion layer. The under bump metallurgy material of thisembodiment also includes a barrier layer plated on top of the conductionlayer and a sacrificial layer plated on top of the barrier layer. Theconduction layer of this embodiment includes a trench formed therein,the trench contacting a portion of the barrier layer and blocking a pathof intermetallic formation between the conduction layer and thesacrificial layer.

Another embodiment of the present invention is directed to a method ofmanufacturing a lead-free solder bump connection. The method of thisembodiment includes sputtering an adhesion layer; sputtering aconduction layer on top of the adhesion layer; coating the conductionlayer with a layer of photo-resist; developing the photo-resist to leavea predetermined pattern of photo-resist on a top surface of theconduction layer; forming a barrier layer on top of the conductionlayer; forming a sacrificial layer on top of the barrier layer; washingthe lead-free solder bump connection with a solvent to remove at least aportion of the remaining photo-resist; and etching the lead-free solderbump connection to form a trench in the conduction layer in a locationthat underlies an edge of the barrier layer.

Additional features and advantages are realized through the techniquesof the present invention. Other embodiments and aspects of the inventionare described in detail herein and are considered a part of the claimedinvention. For a better understanding of the invention with advantagesand features, refer to the description and to the drawings.

BRIEF DESCRIPTION OF THE DRAWINGS

The subject matter which is regarded as the invention is particularlypointed out and distinctly claimed in the claims at the conclusion ofthe specification. The foregoing and other objects, features, andadvantages of the invention are apparent from the following detaileddescription taken in conjunction with the accompanying drawings inwhich:

FIG. 1 shows a lead-free under bump metallurgy;

FIG. 2 shows an embodiment of a lead-free under bump metallurgyaccording to one embodiment of the present invention;

FIG. 3 shows a method by which a lead-free under bump metallurgyaccording to one embodiment of the present invention may be created; and

FIGS. 4A-4D show side views of various stages of the creation of anunder bump metallurgy according to one embodiment of the presentinvention.

The detailed description explains the preferred embodiments of theinvention, together with advantages and features, by way of example withreference to the drawings.

DETAILED DESCRIPTION OF THE INVENTION

Aspects of the present invention are directed to a UBM for lead-freeapplications having reduced intermetallic formations and methods formanufacturing the same. In one embodiment, the present inventionincludes a conduction layer (typically made of copper) that has trenchcreated therein that prevents or reduces the formation ofintermetallics.

FIG. 1 shows a cutaway side view of a typical UBM structure 100. The UBMstructure 100 includes an adhesion layer 102. This adhesion layer 102 ismade of titanium tungsten, for example. Of course, other metals may beused for this layer. As one of ordinary skill in the art will readilyrealize this adhesion layer 102 may be used to adhere to an underlayer(not shown) of polyimide. The adhesion layer 102 is deposited using asputtering technique. Of course, the adhesion layer could be created inany manner including, for example, electroplating.

On top of the adhesion layer 102 is a conduction layer 104, which may beused to distribute electrical energy or signals over the surface of awafer. The conduction layer 104 may, as one of ordinary skill in the artwill readily realize, be made of copper. Similar to the adhesion layer102, the conduction layer 104 is deposited using a sputtering technique.Alternatively, the conduction layer 104 may be formed by alternativetechniques such as, for example, electroplating.

A barrier layer 106 is then electroplated on top of the conduction layer104. The barrier layer 106 may include, in some instances, a nickelmaterial. The barrier layer 106 may be formed in other manners. Forexample, the barrier layer 106 may be formed using sputteringtechniques.

Above the barrier layer 106, a sacrificial layer 108 is formed. Thesacrificial layer 108 is configured to receive a lead-free solder ball.The sacrificial layer 108 includes copper and is formed byelectroplating techniques. However, the sacrificial layer 108 mayultimately diffuse into a lead-free solder ball (typically composed oftin or a tin alloy) placed thereon.

As shown in FIG. 1, portions of the conduction layer 104 may defusealong the path represented by arrow A into the sacrificial layer 108.This may cause intermetallics to form in and around the edges of thesacrificial layer 108. The formation of intermetallics may, in somecases, cause the sacrificial layer to become more brittle or otherwiseunreliable in that the surface of area of the sacrificial layer may bereduced. This may lead, in some instances, to a weaker bond between thesolder ball and the BLM 100 resulting in a failure.

FIG. 2 shows a BLM structure 200 according to one embodiment of thepresent invention. The BLM structure 200 includes an intermetallicblocking trench formed in one of its layers such that the trench blocksor reduces the diffusion of a conduction layer into the solder ballwhich might otherwise lead to a less reliable bond between the solderball and the BLM structure 200.

The BLM structure 200 may include an adhesion layer 202. This adhesionlayer 202 may, in some embodiments, be made of titanium tungsten. Ofcourse, other metals may be used for this layer. As one of ordinaryskill in the art will readily realize, the adhesion layer 202 may beused to adhere or otherwise connect to an under-layer (not shown) ofpolyimide. In some embodiments the adhesion layer 202 is deposited usinga sputtering technique. Of course, the adhesion layer could be createdin any manner including, for example, electroplating.

The BLM structure 200 may also include a conduction layer 204. Thisconduction layer 204 may be used to distribute electrical energy orsignals over the surface of a wafer. The conduction layer 204 may, asone of ordinary skill in the art will readily realize, be made ofcopper. In some embodiments, the conduction layer 204 is deposited usinga sputtering technique. Of course, the conduction layer 204 could becreated in any manner including, for example, electroplating.

The conduction layer 204 may include a trench 210 located therein. Thetrench 210 may serve to keep the conduction layer 204 from formingintermetallics with the substances in the sacrificial layer 208 or thesolder balls which are ultimately place on the sacrificial layer 208. Insome embodiments, the trench 210 is circular, when viewed from above, inshape. Of course, the trench 210 could be of any shape.

The BLM structure 200 may also include a barrier layer 206. The barrierlayer 206 may be plated on top of the conduction layer 204 or otherwisebe formed thereon. In some embodiments this layer may be nickel. An edgeof the conduction layer may, in some embodiments, extend over a portionof the width of the trench 210. Being so arranged, the conduction layer204 may effectively be blocked from diffusing into the sacrificial layer208 (or the solder ball ultimately placed thereon).

The BLM structure 200 may also include a sacrificial layer 208 above thebarrier layer 206. The sacrificial layer 208 is configured to receive alead-free solder ball. In some embodiments, the sacrificial layer 208 iscomposed of copper and is formed by electroplating techniques. As one ofordinary skill in the art will readily realize, the sacrificial layer108 may ultimately diffuse into a lead-free solder ball (typicallycomposed of tin or a tin alloy) placed thereon.

FIG. 3 shows a method by which a UBM according to the present inventionmay be created. The process begins at block 302 where an adhesion layeris deposited. This adhesion layer may be deposited by well knownsputtering techniques or any other technique. In some embodiments thisadhesion layer is made of titanium tungsten.

In block 304 a conduction layer is deposited on top of the adhesionlayer. The conduction layer may be made of, for example, copper. As withthe adhesion layer, the conduction layer may be deposited by well knownsputtering techniques or any other technique.

At block 306, photo-resist is deposited on top of the conduction layer.The deposition of photo-resist is well known in the art. At block 308,photolithography is performed on the photo-resist to create via in thephoto-resist on top of the conduction layer.

FIG. 4A shows a cut-away side view of a BLM structure 318 as it mayexist after step 308 has been performed. The BLM structure 318 includesan adhesion layer 202 and a conduction layer 204. A layer ofphoto-resist 320 has been formed on top of the conduction layer 204 and,as stated above, photolithography has been performed on the layer ofphoto-resist 320 to form a via 360 to receive later formed layers.

In some embodiments, the photolithography process may be controlled sothat portions of the photo-resist that was to be removed may remain. Asshown in FIG. 3B, and in practice, residual photo-resist particles 322may exist near the walls of the receiving depression 324. In someembodiments, these residual photo-resist particles 322 may bebeneficial. In particular, when they are removed they may create abridge through a barrier layer formed on top of the conduction layer 204to allow an etch chemical to access the conduction layer to create atrench therein.

Referring again to FIG. 3, at block 310 a barrier layer is created ontop of the conduction layer and the photo-resist still remaining fromthe photolithography process. This barrier layer may be created in manymanners. For example the barrier layer may be created by electroplating.In one embodiment this barrier layer is composed of nickel.

In block 312 a sacrificial layer is placed on top of the barrier layer312. The creation of a sacrificial layer may be done by electroplatingand may include plating copper onto the top of the barrier layer.

FIG. 4B shows a cut-away side view of a BLM structure 318 after abarrier layer 206 has been formed on the conduction layer 204 and asacrificial layer 208 has been formed on top of the conduction layer. Asshown, the BLM structure 318 still includes photo-resist layer 320 andthe residual photo-resist particles 322. As shown, the barrier layer 208includes a wing portion 324. This wing portion 324 is a part of thebarrier layer 206 that slipped under the photo-resist 320 during theformation of the barrier layer 206. Such an occurrence is well known inthe art. However, the presence of the residual photo-resist particles322 during the formation process cause the barrier layer 206 to beformed such that it includes photo-resist pockets which are formed bythe photo-resist particles 322. These pockets extend through the barrierlayer 106.

Referring again to FIG. 3, at block 314 a photo-resist wash isconducted. This photo-resist wash removes the remaining photo-resist onthe outsides of the barrier and sacrificial layers. This photo-resistwash also removes all of the photo-resist from any photo-resist pocketsformed in the barrier layer by the residual photo resists particles. Theremoval of the photo-resist in the photo-resists pockets creates achannel through the barrier layer.

FIG. 4C shows a cut-away side view of a BLM structure 318 after thephoto-resist layer and the residual photo-resist particles have beenremoved by, for example, a photo-resist wash or other techniques. Thebarrier layer 206 includes channels 340 that are a path through thebarrier layer to the conduction layer 204. The channels 340 were createdby the removal of the residual photo-resist particles during thephoto-resist wash.

Referring again to FIG. 3, a chemical etching process may be performedat block 316. This process may be two fold. The first step of thisprocess includes a first etching process that etches the material of theconduction layer. This process may include exposing the BLM 318 to achemical that dissolves or otherwise etches copper. The second processmay include exposing the BLM to a process that dissolves or otherwiseetches the material the adhesion layer is formed of.

FIG. 4D shows a cut-away side view of a BLM structure 318 after anetching process that dissolves the conduction layer 204 has beenperformed. As shown, only a portion of the adhesion layer 204 has beendissolved. However, the process could be conducted in such a manner thatall of the conduction layer 204 that is exposed to the etching processis dissolved. The etching chemicals used in the etching process passthrough the channels 340 so that they may contact the conduction layer204. The contact between the etching chemical that passes through thechannels 340 and the conduction layer 204 results in the creation of thetrench 314. As discussed above, the trench 314 may serve to reducediffusion of the conduction layer 204 into the sacrificial layer 208 andthereby reduce the formation of intermetallics.

While the preferred embodiment to the invention has been described, itwill be understood that those skilled in the art, both now and in thefuture, may make various improvements and enhancements which fall withinthe scope of the claims which follow. These claims should be construedto maintain the proper protection for the invention first described.

1. An under bump metallurgy material comprising: an adhesion layer; aconduction layer formed on top of the adhesion layer; a barrier layerplated on top of the conduction layer; and a sacrificial layer plated ontop of the barrier layer; wherein the conduction layer includes a trenchformed therein, the trench contacting a portion of the barrier layer andblocking a path of intermetallic formation between the conduction layerand the sacrificial layer.
 2. The under bump metallurgy material ofclaim 1, wherein the conduction layer is composed of copper.
 3. Theunder bump metallurgy material of claim 2, wherein the adhesion layer iscomposed of titanium.
 4. The under bump metallurgy material of claim ofclaim 2, wherein the barrier layer is composed of nickel.
 5. The underbump metallurgy material of claim of claim 4, wherein the sacrificiallayer is composed of copper.
 6. The under bump metallurgy material ofclaim 2, wherein the trench is etched into the conduction layer.
 7. Theunder bump metallurgy material of claim 6, wherein the trench is etchedinto the conduction layer using photolithography.
 8. (canceled) 9.(canceled)
 10. (canceled)
 11. (canceled)
 12. (canceled)